Photometer.



PATENTED JUNE 4, 1907.

0. H. WILLIAMS.

PHOTOMBTBR. AIPLIOATIOI mm nov. a. 1m.

U ITED STATES PATENT OFFICE.

; CHARLES H. WILLIAMS, OF MILTON, MASSACHUSETTS.

' 'FHOTOMETER.

Specification of Letters Patent.

Patented June 4, 1907.

A li atio fil d Hovembir 24, 1905. Serial H0. 288,898.

1'0 al l ,urh am, it may concern.-

Be it known that I, Cnanuzs H iViLpuns, a citizen of the United States, residing in Milton, in the county of Norfolk and btate of the fol Massachusetts, have invented a new and useful Im u'ovcnientin Photometers, of which lowing is a specification.

This invention relates to that class of photometers intended for use in measuring the intensity, the relative intensities or the relative illuminating power of terrestrial lights, and it is designed more particularly, to measure the amount of light coming from a distant; signal; to compare white, red, green, yellow, or other lights with each other as to their photometric value; to measure electric lights in a building or elsewhere, without removing them from their. receptacles, for the purpose of ascertaining whether they are falling below their standard of brightness; to ascertain the candlewer' of gas-lights; to compare terrestrial li ts with a standard fixed value based on stellar magnitudes; and in general to produce a compact and accurate standard instrument for the measurement of terrestrial lights.

'In carrving out my invention, I employ a developed photographic plate on which is a film increasing in density from one end to the other, such a plate not being new in itself considered, as it has been used in astronomical measurements at the Harvard Observatory in (.ambridge, Massachusetts. I provide this plate (which is much longer than it is wide) with a suitable frame furnished with 1 a handle at one end, and inc-lose it in a case of similar shape, in whlch the plate is adapted 5c is nearer the holes.

-to slide but is prevented from complete separation therefrom. The case is provided on its opposite sides with coincident or registering holes through vhich the light to be tested is viewed by the eye, and on its front side with another opening through which a graduated scale on the plate is rendered visible. One end of the plate is provided with a sliding removable co :er providcd at its outer end with a loop or hail of shape to fit transversely over or around the case and hold the cover at right angles with that end of the case which The cover when in this position o crates as an eye-guard or shade and is held therein preferably by means of a "spring which also operates as a'stop to prel vent the plate from dropping out of or being drawn from the case.

The nature of the invention is fully described below, and illustrated in the accompanying rawing, in which n.-

Figure 1 is a front elevation of my photometer with the cover in position thereon and extending over the holes or openings in the case. Fig.2 is a perspective view of the photonaeter as it appears in actual use, the cover being n position to operate as an eye-guard. Fig. 3 1s a lon itudinal vertical section of the device with the arts in the position indicated in F ig. 1. lg. 4 is a cross vertical section taken on line 4-4, Fig. 2.

Similar letters of reference indicate corresponding parts,

a represents a developed photographic plate provided with a film b which increases in density from one end toward the other (the drawing indicating the increase of density as being toward the left) said plate being preferably long and narrow, and bei furnished with a suitable metallic frame 0. The right end of this plate is provided with a handle d of any suitable construction, adapted to extend a little from that end of the casethe 8o handle illustrated consisting merely of a metallic fold e thickened or rounded at its outer end as shown at e. The lower edge of the framed plate has secured to it adhcsivcly, or m any suitable manner, a narrow strip f provided with a suitable scale. This framei developed photographic plate is inclosed slidingly in a case 9 corresponding in shape to the plate, said case being open at its right end, and provided at that end with a sliding o removable cover 12-, closed atits right end, and furnished at that end with a sta 1e sha ed bail or loop whose outer portion is pre crably straight and at a distance from the right end of the cover which corresponds 5 substantiallv with the thickness of the case g, said portion is bein connected with the top and bottom edges of the cover Ii. by means of the legs k.

The case is provided with three holes or alpertures, viz., a hole I in the front wall of t 1e case as it is used, said hole being preferabl somewhat elongated, and registering wit the scale 1': and two coincident or registering holes n in the front and rear walls, 0 posite the lilm b on the plate, and direct y BEST AVAILABLE COPY above the center of the hole I.

near the inner end of the A spring p has one end secured to the to edge of the case, and its free end p exten 5 toward the right. and down over the end of the case and bears normally on the upper edge of the frame 0 of the plate. On said edge of the. frame there is secured a small stop-bead 8 late, which by striking the booked and 1 o thc'spring, prevents the plate from falling out of or being drawn inadvertently from the case.

In practical operation, when the instrument is to be used for any of the purposes hereinbel'ore recited, the cover I: is removed from the position illustrated in Fi 1, and its bail k, Ir is sli ied over the end of the case, beiw held iirinly in position by the spring 7;, in which position the cover extends at right angles from the case and is substantially flush with the right end thereof, as shown in Fig. 2. The photometer case is then held horizontally before the eyes, resting on the nose, and the coincident openings 11 are brought before the right or left eye (as preferred) of the observer the eye be e shaded at the end next the holes n by s cover. The '"htto be measured is then brought into t is field of view, as near the center of the field as practicable, and the case is so held as to kee this light in the field during the test. 'itli the hand of the side corresponding to the eye used, the glass photometric plate is slowly withdrawn from the case, and as it is withdrawn the thickness of the photographic film b, as it appears between the ho cs 12-, increases in densitv, and the light appears to gradually diminish until it finally disap ars. The moment the light is extinguishecfhy the film, the hand releases the photometric plate which is held in position by the down-turned end p of the spring p, the instrument is removed from the face, and the scale "indicates through the opening I the point oi" extinction on the film for that light. By testiw another l' ht in the same manner and tea g the sea e, comlpara-tive values of the two lights can be easi y determined.

In practice. the instrument is made of convenient size and shape to be easily carried in the pocket, and it is so sim le in construction and use that those w o are unaccustomed to scientific instruments can measure signal, electric, gas and other terrestrial lights without difficulty, and with results which will compare iavorablv in photometric value with those produced ny more expensive instruments.

It is evident that the case may be reversed, the plate drawn from its left end, and the cover applied to the same end, if desired, and the openings 1 and 12- located near the left instead of the right end.

Having thus fully described my invention, what 1 claim, and desire to secure by Letters Patent, is:-

1. In a photometer, a developed photographic plate provided with a film increasing in density from near one end toward the other: a scale on said plate: a case adapted to hold said plate but allow it to s ide in the line of direction of the increase of density in the film, said case being provided with coincident holes in its walls on opposite sides of the plate, and with an opening opposite the scale; a cover adapted to be applied to one end of the case; and a bail or loop extending from the outer end of the cover, and of shape to embrace the ease and hold said cover at an angle thereto when the photometer is in use, for the purpose set forth.

2. In a photometer, a developed photographic plate provided with a film increasing in density from near one end toward the other; a scale on said plate; a case adapted to hold said plate but allow it to slide in the line of direction of the increase of density in the film, said case being provided with coincident holes in its walls on opposite sides of the plate, and with an opening opposite the scale; a cover adapted to be Slld over the open end of the case; a bail or loop extending from the closed end of the cover and adapted to embrace the case and hold said cover at substantially right angles thereto when the photometer is in use; and a spring secured to the case and extending when the cover is thus applied, between the ease and the bail and bearing on the plate, thereby preventing accidental relative movement of the plate and case and of the case and cover, for the purpose set forth.

In testimony whereof I have signed my name to this specification in the presence of two subscribing witnesses.

CHARLES H. WILLIAMS.

Witnesses:

Haxar W Wrnuans, A. K. Hoon.

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